Animals

What is an Animal?

• Animal – multicellular eukaryotic heterotrophs whose cells lack walls

• 95% of all animal species are invertebrates (no backbone or vertebral column

Embryology

• Embryology – early development• Zygote undergoes series of divisions to become

a blastula • Blastula - Hollow ball of cells• Gastrula - Blastula folds on itself, forming a

single opening (blastopore) and the gastrula.– Blastopore leads into a central tube that runs the

length of the developing embryo. Tube becomes the digestive tract.

The Fertilized Egg & Cleavage

• Yolk~ nutrients stored in the egg

• Vegetal pole~ side of egg with high yolk concentration

• Animal pole ~ side of egg with low yolk concentration

• Blastula~hollow ball stage of development

Gastrulation• Gastrula~ 2 layered, cup-shaped

embryonic stage

• 3 Embryonic germ layers: • Ectoderm~ outer layer; epidermis;

nervous system, etc.

• Endoderm~ inner layer; digestive tract and associated organs; respiratory, etc.

• Mesoderm~skeletal; muscular; excretory, etc.

• Invagination~ gastrula buckling process to create the...– Archenteron~ primitive gut

– Blastopore~ open end of archenteron

Protostomes and Deuterostomes

• Protosomes – an animal whose mouth is formed by the blastopore (most invertebrates)

• Deuterosomes – an animal whose anus is formed by the blastopore ( echinoderms and all vertebrates)

Animal Embryology

• Protostome-Deuterostome dichotomy among coelomates: protostomes (mollusks, annelids, arthropods); deuterostomes (echinoderms, chordates)

• a) cleavage: protostomes~ spiral and determinate; deuterotomes~ radial and indeterminate

• b) coelom (body cavity) formation: protostomes~ schizocoelous; deuterostomes~ enterocoelous

• c) blastopore fate: protostomes~ mouth from blastopore; deuterostomes~ anus from blastopore

Body Cavity

• Body cavity (coelom) formation – fluid filled space that lies between the digestive tract and the body wall. – Allow internal organs to be suspended –

helpful during movement. – Provide room for internal organs to specialize

and enlarge.

Body Symmetry

• Asymmetrical – no symmetry (sponge)• Radial – like a bicycle wheel, no matter how you

divide the animal with imaginary planes you get two equal halves (jellyfish)

• Bilateral – a single imaginary plane can split the animal in half (crayfish, human)– Cephalization – animals with bilateral symmetry have

concentrated sense organs and nerve cells at the front end of the body (head)

Binomial Nomenclature

• The Linnaeus System works by placing each organism into a layered hierarchy of groups. Each group at a given layer is composed of a set of groups from the layer directly below. Simply knowing the two-part scientific name makes it possible to determine the other six layers.

Linnaeus System

• The groupings (taxa) of taxonomy from most general to most specific are: • Kingdom • Phylum (animals) or Division (plants) • Class • Order • Family • Genus • Species

Fig. 23-1, p. 485

DOMAINEukarya

KINGDOMAnimalia

PHYLUMChordata

CLASSMammalia

ORDERCarnivora

FAMILYFelidae

GENUSFelis

SPECIESFelis catus

Domain Comparison

Bacteria Archaea Eukarya

Prokaryote Prokaryote Eukaryote

Unique bacterial rRNA nucleotide sequence

Unique archaean rRNA nucleotide sequence

Cell walls with peptidoglycan

Cell walls with NO peptidoglycan

Cell walls in plants and fungi

“extremophiles” Cell walls resistant to osmotic shock

Modern Evolutionary Classification

• If you lived in the time of Linnaeus, how would you have classified dolphins? Barnacles and crabs?

• Phylogeny – study of evolutionary relationships o Species in a genus have a common ancestor o Genuses in a family have a common ancestor, etc. o Conclusion: the higher the taxon, the further back the common ancestor

Phylum: Porifera (“pore bearer”)• Sponges• Asymmetrical; no coelom; no organs• Sessile (attached to bottom)• Spongocoel (central cavity)• Osculum (large opening)• Choanocytes (flagellated collar cells)• Hermaphroditic (produce both sperm and eggs)

Phylum: Cnidaria

• hydra, jellies, sea anemones, corals

• Radial symmetry; no coelom• No mesoderm; gastrovascular

cavity (GVC) (sac with a central digestive cavity)

• Hydrostatic skeleton (fluid held under pressure)

• Polyps and medusa forms• Cnidocytes (cells used for

defense and prey capture)• Nematocysts (stinging

capsule)

Phylum: Platyhelminthes

• flatworms, flukes, tapeworms

• Bilateral; no coelom• Predators, scavengers,

parasites• Triplobastic; mesoderm but,

GVC with only one opening• Some cephalization• Many pathogens

(Schistosoma, Cestodidias)

Phylum: Nemotoda

• roundworms• Very widespread group of

animals (900,000 sp. ?)• Cuticle (tough

exoskeleton)• Decomposition and

nutrient cycling• Complete digestive track;

no circulatory system• Trichinella spiralis

Phylum: Mollusca

• snails, slugs, squid, octopus, clams, oysters, chiton

• True coelom• Soft body protected by a hard

shell of calcium carbonate• Foot (movement), visceral

mass (internal organs); mantle (secretes shell); radula (rasp-like scraping organ)

• Ciliated trochophore larvae (related to Annelida?)

Phylum: Annelida

• earthworms, leeches, marine worms

• True body segmentation (specialization of body regions)

• Closed circulatory system• Metanephridia: excretory

tubes• “Brainlike” cerebral ganglia• Hermaphrodites, but cross-

fertilize

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Phylum: Arthropoda

• trilobites (extinct); crustaceans (crabs, lobsters, shrimps); spiders, scorpions, ticks (arachnids); insects (entomology)

• 2 out of every 3 organisms (most successful of all phyla)

• Segmentation, hard exoskeleton (cuticle)~ molting, jointed appendages; open circulatory system (hemolymph); extensive cephalization

Arthropoda: Insect characteristics

• Outnumber all other forms of life combined

• Malpighian tubules: outpocketings of the digestive tract (excretion)

• Tracheal system: branched tubes that infiltrate the body (gas exchange)

• Metamorphosis…...

• •incomplete: young resemble adults, then molt into adulthood (grasshoppers)

• •complete: larval stages (looks different than adult); larva to adult through pupal stage

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Phylum: Echinodermata

• sea stars, sea urchins, sand dollars, sea lilies, sea cucumbers, sea daisies

• Deuterostomes

• Spiny skin; sessile or slow moving

• Often pentaradial

• Water vascular system by hydraulic canals (tube feet)

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Chordates

• Notochord: longitudinal, flexible rod located between the digestive and the nerve cord

• Dorsal, hollow nerve cord; eventually develops into the brain and spinal cord

• Pharyngeal slits; become modified for gas exchange, jaw support, and/or hearing

• Muscular, postanal tail

Invertebrate chordates• Both suspension feeders…..• Subphy: Urochordata (tunicates; sea squirt); mostly sessile & marine• Subphy: Cephalochordata (lancelets); marine, sand dwellers• Importance: vertebrates closest relatives; in the fossil record, appear 50

million years before first vertebrate

Subphylum: Vertebrata

• Retain chordate characteristics with specializations….

• Neural crest: group of embryonic cells near dorsal margins of closing neural tube

• Pronounced cephalization: concentration of sensory and neural equipment in the head

• Cranium and vertebral column • Closed circulatory system with a

ventral chambered heart

Vertebrate diversity• Phy: Chordata• Subphy: Vertebrata• Superclass: Agnatha~

jawless vertebrates (hagfish, lampreys)

• Superclass: • Gnathostomata~jawed

vertebrates with 2 sets of

paired appendages; including tetrapods (‘4-footed’) and amniotes (shelled egg)

Superclass Agnatha

• Jawless vertebrates• Most primitive, living

vertebrates• lamprey and hagfish • Lack paired

appendages; cartilaginous skeleton; notochord throughout life; rasping mouth

Superclass Gnathostomata, I• Class: Chondrichthyes~ Sharks, skates, rays

• Cartilaginous fishes; well developed jaws and paired fins; continual water flow over gills (gas exchange); lateral line system (water pressure changes)

• Life cycles:

• Oviparous- eggs hatch outside mother’s body

• Ovoviviparous- retain fertilized eggs; nourished by egg yolk; young born live

• Viviparous- young develop within uterus; nourished by placenta

Superclass Gnathostomata, II• Class: Osteichthyes• Ossified (bony) endoskeleton; scales operculum(gill covering); swim

bladder (buoyancy)• Most numerous vertebrate• Ray-fined (fins supported by long, flexible rays): bass, trout, perch,

tuna, herring• Lobe-finned (fins supported by body skeleton extensions): coelocanth• Lungfishes (gills and lungs): Australian lungfish (aestivation)

Superclass Gnathostomata, III• Class: Amphibia• 1st tetrapods on land• Frogs, toads, salamanders, caecilians• Metamorphosis; lack shelled egg;

moist skin for gas exchange

Superclass Gnathostomata, IV• Class: Reptilia• Lizards, snakes, turtles, and crocodilians• Amniote (shelled) egg with extraembryonic membranes (gas exchange,

waste storage, nutrient transfer); absence of feathers, hair, and mammary glands; ectothermic; scales with protein keratin (waterproof); lungs; ectothermic (dinosaurs endothermic?)

Superclass Gnathostomata, V• Class: Aves

• Birds

• Flight adaptations: wings (honeycombed bone); feathers (keratin); toothless; one ovary

• Evolved from reptiles (amniote egg and leg scales); endothermic (4-chambered heart)

• Archaeopteryx (stemmed from an ancestor that gave rise to birds)

Superclass Gnathostomata, VI• Class: Mammalia• Mammary glands; hair (keratin);

endothermic; 4-chambered heart;

large brains; teeth differentiation• Evolved from reptilian stock

before birds• Monotremes (egg-laying): platypus• Marsupials (pouch): opossums,

kangaroos, koalas• Eutherian (placenta):

all other mammals